Radio receiving system



March 31, 1936. E. R. PFAFF ET AL RADIO RECEIVING SYSTEM Filed Jan. 9, 193:5

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RADIO RECEIVING SYSTEM Filed Jan. 9,v 1953 2 Sheets-Sheet 2 :inventors kfw?, QM

(ttornegS Patented Mar. 31, 1936 UNI-TE S RADIO RECEIVING SYSTEM Application January 9, 1933, SerialNo. 650,820

Claims.

This invention relates to improvements in radio receivers and more particularly to a receiver of the superheterodyne type adapted to receive radioV signals with fidelity, selectivity and sensir tivity over a broad range of frequencies such as the broadcast and short wave spectrums.

Heretofore efforts have been made to construct radio receiving sets which would receive signals offlow frequency as well as those of high frequency. Receiving sets have been proposed in which one complete circuit was employed for low frequency signals and another independent circuit was employed for high frequency signals. Each circuit was independent of the other or others and was tuned independently of the other circuits. This involved separate tuning apparatus for each circuit and made the set unnecessarily cumbersome.

Other attempts have been made.. in whichit Was proposed to use a single tuned circuit (the oscillator circuit) for tuning the receiver to resonance to the particular frequency which it wask in -sfuch systems.

Other attempts included the provision of a plurality of individual manually changed plug-in coils.

But such a receiver requires that it and the coils; be accessible for such manual plugging-in. ATheshifting from one wave band to another in this receiver involved time and caused annoyance because the coils were not always easily aligned with the contacts. A succeeding effort was made to avoid the foregoing disadvantages whereby the coils were stationarily mounted and leads from the coils were carried to a multipolar switch so arranged that the individual coils could be selected by a switch unit.

This, however, had a disadvantage wherein althouglrtime and annoyance were. cured the new arrangement caused a considerable loss in eiciency because of the long leads necessary to connect the coils to the switch and due to the each circuit was a further disadvantage presentv (Cl. Z50-20) fact that the coils took up considerable space and could not be arranged compactly and placed in the best place for ecient reception.

We have found that it is'possible to maintain. substantiallylthe same selectivity, sensitivity, and efficiency of reception throughout substantially` the entire radio spectrum without encountering any of the previous disadvantages such as cumbersomeness, more compact construction, manually manipulated coils, separate tuning devices, variable sensitivity, selectivity, and efficiency, and have accomplished these results by a new combination of elements and a new mode of operation. The means and method by which these new and improved results are obtained may be readily visualized and understood by a brief description of our invention.

Generally speaking, we accomplish the foregoing results as follows: we provide a super-` heterodyne circuit for long waves and provide means .for selectively adapting the receiver for the various short wave bands. We provide simultaneously actuated tuning condensers for the oscillator and detector circuits of the superheterodyne which we cause to track with each other for all frequencies. We provide a plurality of inductances whichare respectively adapted to receive signals on different frequency bands and mount them and ideally and compactly locate them so that by a single simple mechanical means they may automatically be selectively included in the oscillator and detector circuits to obtain the best electrical characteristics therefrom.

The means used to couple selectively the inductances into the circuits may also simultaneously change the tuned antennae circuit, inv case it was tuned, to an untuned antennae. circuit, change the capacitances which tune the inductances and change the nature of the coupling between the circuits.

By means of the foregoing parts and combinations of parts we have provided a receiver for receiving radio signals throughout the entire radiospectrum having oscillator and detector condensers controllable simultaneously by a single means to tune the receiver to a signal eiiiciently, with delity and selectivity and sensitivity, and having common control means for selectively coupling different inductances into the oscillator and detector circuits, change the method of and apparatus for coupling the circuits, substitute the different capacities for tuning the inductances, and, if desiredy change the antennae circuit.

The. invention together with its various advantages will be more apparent from the following description which together with the accompanying drawings forms a part of this specication.

In the drawings:

Figure 1 is a circuit diagram of a complete receiver embodying the invention;

Figure 2 is a circuit diagram showing the parts of the circuit of Figure 1 used for the reception of the broadcast band and wherein the parts of Figure 1 which are not used have been eliminated;

Figure 3 is a circuit diagram similar to that of Figure 2 showing the parts of the circuit of Figure 1 used for the reception of the short waves;

Figure 4 is a diagram illustrating a portion of the circuit and their couplings;

Figure 5 is a diagrammatic view of a modified form of antenna circuit.

Referring particularly to Figure l there is shown a circuit diagram for a radio receiver wherein is provided an antenna circuit A, a radio frequencyamplifying circuit B, a first detector C, an intermediate amplifier D, a second detector E, and an audio frequency amplifier F. An inductance changer is also shown and includes a section Y with a plurality of inductances YB and YG for the radio frequency circuit and the local oscillator. A changeable coupling for connecting the oscillator to the radio frequency or detector circuit is illustrated at YC. A section Z is provided and contains a series of fixed contacts connected into the circuit into contactwith which the various inductances may be selectively shifted. Such an inductance changer and switch is shown and described in the co-pending application of Ernest R. Pfaff, Clifford L. Coon, and George Roethel, Jr., filed on October 26, 1932, Serial No. 639,728; now Patent No. 1,986,525 granted January 1, 1935.

For broadcast reception, on wave lengths between 200 and 550 meters, the antenna circuit includes the antenna I directly connected by a lead to a primary antenna coil 2. The antenna coil 2 is tapped and a switch 3 connects the same to the ground and is adapted to include or exclude turns of the antenna coil acting as a local distance switch. A secondary 4 is inductively coupled to the coil 2 and is tuned by condensers 5. One end of the secondary is grounded as well as the cathode at 5 of the radio frequency tube. It is of course within the purview of `this invention to also providean untuned antenna circuit for long waves should it be so desired.

' A switch 1 is adapted to connect the grid of the first radio frequency tube selectively to the antenna I for short wave reception, or to the secondary 4 for long wave reception. The plate of the first radio frequency tube is capacitively coupled at 8 to the radio frequency inductance 9. The lead coupling the capacity to the plate and to the secondary 9 extends to a radio frequency choke I and is also connected by a lead and capacity II to the fixed contact I2 which is one of a plurality of xed contacts I2 to I1 inclusive. This lead is only used for short wave reception.

A lead I8 connects the inductance 9 to the contact IB. Contacts I5, I6 and I1 are adapted to be connected together when the movable contacts I5', I6', and I1', which are connected to each other, are shifted into contact therewith. This results in connecting the other end of the inductance 9 to the tuning condenser 29 through the lead 2| which connects to the fixed contact I5. Thustlie secondary 9 may be tuned by the condenser 29. `The grid lead 22 of the first detector C is coupled direct to the secondary 9 by the lead 4I8 through the contacts I6 and I1.

The oscillator circuit for introducing a heterodyne into the system is coupled to the secondary 9 by a coupling coil 33. The oscillator includes the thermionic tube as shown in section YG and comprises a secondary inductance 23 in the grid circuit of the tube and is adapted to be tuned by the variable capacity 25 in series with a padding condenser 26. Fixed contacts 21 to 32 inclusive are provided with the fixed unit. The inductances in movable section YG are adapted to be selectively shifted into contact with the fixed contacts 21 to 32 inclusive. For the purpose of this description it should be assumed that the movable inductances have been shifted so that the lower line of movable inductances in the section YG are in electrical contact with the fixed contacts. The other end of the secondary oscillator inductance is grounded through contact 30. The plate coil 43 is connected into the oscillator plate circuit through the contact 3| by the lead 34 and through the oscillator coupling coil 33 to the B supply. The other end of the plate coil is connected through contact 32 and'lead'to the plate of oscillator tube. The feed back from plate coil 43 into the grid coil 23 causes sustained' oscillations in plate circuit of the oscillator which` are tuned to desired frequency by the condensers 25 and 26. The oscillations thus generated are introduced into the radio frequency circuit Brby the inductive relation between the coupling coil 33 and the inductance 9 and thence into the detector at C.

The output or heterodyne from the detector C is amplified by the intermediate frequency amplifier D, is then demodulated at E, and then amplified to audio frequency at F.

The foregoing arrangement is also illustrated in Figure 2 where for clarity all lines representing circuit connections not used when the receiver is adjusted for this particular band are eliminated.

For short wave reception on the band" immediately below the broadcast band, which for example may include the wave lengths from 60 to 200 meters, the switch 1 is shifted to make contact with the antenna I. This eliminates from the circuit the tuned inductance 4, connecting the antenna to the grid of the radio fre-l quency tube. The primary 3 remains in the circuit. This coupling as well as that about to be described is best shown in Figure 3 which is similar to Figure 2 being the circuit as adjusted for wavelengths between 60 and 200 meters with the connections not used eliminated.

The second line of inductances in the movable section Y are shifted, shifting the broadcast oscillator coils out of the circuit and opening the circuit at contacts I5, I6 and I1. 'Ihe same switch which makes the shift also makes the change in the antenna circuit simultaneously.

The plate of the radiofrequency tube is then connected to B supply through the radio frequency choke I0 and is capacitively coupled by capacity I I to the radio frequency tuning inductance 4D through contact I2 and contact I2", and I5 and I5. The other end of inductance III is connected to ground through contact I3". The contact I5 is also connected to contact I1". 'I'he inductance 4D is then tuned by the capacity 20 which is connected by lead 2| to contact I5 and the other end of the inductance to ground through contact I3". The inductance 40 is also capacitively coupled to the grid coil '23 of Vthe oscillator. The grid coil is tuned by condenser 25 as previously described. The connections for .the plate coil 443 ofthe oscillator `are thesame Vas previously described for broadcast receptions.

'I'he remainder of the circuit remains unchanged .except that oscillator coupling coil 33 -is removed from the circuit by the bi-passing capacity-44 between the grid and plate coil of the oscillator. It is to be noted that the radio frequency inductance 9 together with its coupling to the plate circuit ,I is unused as well as the oscillator coupling coil 33 except to permit B supply flow to the plate of .the oscillator.

'Iheconnection for the wave bands between 23 and 61 meters is made by Ashifting the coils 40', 213 and 43" in connection with the fixed contacts of section Z and is the same circuit arrangement as previously described except that the values of the various. movable inductances are different.

For wave lengths between 15 and 23 meters the circuit `and arrangement is the same except that the radio frequency tuning inductance l40 is tuned by a smaller capacity than the other inductances. This is effected byconnecting the radio frequency coil 40" to contact 14 which couples in the condenser 50 by the lead 5|.

The same is effected in the grid coil 23" of the oscillator which is connected to through contact 21"" to the grid, the said contact also being connected to the capacity 60 through a lead to contact 28"" which is of smaller capacity than that used to tune the other grid coils, the end of the inductance being grounded through 301i!)- In reception on the broadcast band the coupling between the radio frequency stage inductance 9 and the grid inductance 23 of the oscillator is accomplished in the usual manner by the use of an oscillator coupling inductance 33 connected in the plate circuit .of the ,oscillator and inductively coupled to the radio frequency inductance 9. However, this type of coupling is changed when the receiver is adjusted to short Wave reception. As shown in Figure 3 the inductance 9 is omitted from the circuit and in its stead an inductance 40 has been shifted into the circuit. For greater efficiency in reception on high frequencies the characteristics of induc- .tance are different; the inductance in the case being smaller for the higher frequencies. 'Ihe inductance 48 is, however, still tuned by the same condenser 20 as was used on the broadcast. band in the lower frequencies. 'I'he inductances in the oscillator circuit which are shifted into the circuit simultaneously with the radio frequency .in-

ductances are also of different value and are also tuned by the same condenser 25 as was used in the lower frequency reception. However, the coupling between the oscillator and the radio frequency circuit is now different and is obtained by capacitively coupling the grid end of the grid inductances 23' to the radio frequency inductance by means of an adjustable capacitance YC and to the grid of the first detector by lead 22 through the contact Il". The capacitance having once ,been adjusted to provide the desired coupling is left in the same position.

The effect of this couplingand whatwe believe to be the theory of operation is better illustrated by the diagram of Figure 4 wherein the basic parts and the coupling of the two circuits is shown. It will be noticed that the inductances V4ll and 2-3 are respectively tuned by the capaci'- ties 20 and 25. The inductances are also capacitively coupled together by YC, at one end and connected together at the other end by a vcommon ground. Due to this arrangement it will become apparent that the tuning capacity 20 for the inductance 40 of the radio frequency circuit which is coupled to the ends of inductance 4G is also coupled and also tunes the inductance 23', being disposed across the inductance 23' by means of the ground and the capacitance YC. The same is true in the converse order for the capacity and inductance 25 and 23' respectively in the oscillator circuit; that is the tuning of the oscillator inductance also is a function of the tuning of the radio frequency stage inductance. Thus the tuning of the radio VVfrequency stage is a function of the tuning of the oscillator stage and vice versa. The effect of this is, that with properly designed condensers 20 and 25, the two circuits can be made to tune so that the condensers track together and hence a single dial may be used. Although we have shown but a single example of the type coupling used between the circuits it may also be apparent that this coupling may be accomplished in an equivalent manner. That is the same effect might be obtained by the substitution of inductances or the like for the capacitance YC'.

In actual practice the variable capacities 20, 50, 5, B0, and 25 are all operated simultaneously by a single shaft, the capacities 50 and 60 being of substantially less capacity than the others.

By coupling the grid coil of the oscillator to the radio frequency coil and the grid of the rst detector capacitively it is possible to tune the oscillator and radio frequency stages simultaneously with single condensers for each stage without the use of separate dials or single dials with trimmers.

In Figure I have shown a modified form of antenna circuit which may be substituted for that of A in Figure 1 which includes an antenna i for long wave reception and another l' particularly adapted for short wave reception. Either of the antennae may be selectively coupled into the circuit, the short wave antenna being coupled into the circuit when the antenna circuit is changed to an untuned circuit.

For long wave reception the antenna switch is actuated to connect the grid of the first tube with the tuned secondary d of the antenna coupling transformer wherein the circuit is substantially as shown in Figure 2.

When tuning on high frequencies, an antenna I' of desirable characteristics for high frequency may be shifted into the circuit by actuating the switch connected to the grid of the first tube to the other position wherein the entire radio frequency transformer and tuning means are omitted from the circuit and the grid is connected directly to the antenna l'. A grid return is had for the tube through a choke coil 8 to theground. The operation is in effect the same as in Figure 3 except `that an antenna of different characteris tics has been substituted.

Although we have shown the coupling for the tuned oscillator to the radio frequency stage as being accomplished by capacitivelycoupling the grid of the oscillator to the grid of radio frequency stage it also is within the purview of this invention to accomplish substantially this same coupling capacitively with other parts of the two tuned circuits. Such effect might be accomplished by coupling the cathodes of the two tuned circuits together.

We claim as our invention: 1. In a radio receiver, a main circuit and two tuned circuits each including an inductance and a variable capacity and having their output connected to the input of the main circuit, means to electrically couple said tuned circuits together,

switching means for simultaneously changing the inductances of said tuned circuits and changing the coupling means between the tuned circuits when the inductances are changed.

2. In a radio receiving system, a main circuit including an intermediate frequency amplifier, a detector and an audio frequency amplifier; a subsidiary long wave circuit comprising an antenna circuit, a radio frequency circuit, a mixer circuit and an oscillator circuit inductively coupled to said mixer circuit; a subsidiary short Wave circuit'comprising an antenna circuit, a radio frequency circuit, a mixer circuit and an oscillator circuit capacitively coupled to the mixer; means cooperative with both subsidiary circuits for se- 'lectively connecting one of said subsidiary circuits to the main circuit and disconnecting the other of said subsidiary circuits from the main circuit.

v 3. In a radio receiving system, a main circuit including an intermediate frequency amplifier,

a second detector and an audio frequency amplifier, a subsidiary long wave circuit comprising an antenna circuit, a radio frequency circuit, a mixer circuit and an oscillator circuit inductively couthe main circuit, means common to both subsidiary circuits to tune either when connected with the main circuit.

' 4. In a radio receiving circuit comprising a short wave tuner and a long wave tuner, an intermediate frequency amplifier, a detector and an audio frequency amplifier common to both tuners, said long wave tuner comprising a tuned antenna circuit, a tuned radio frequency circuit, a tuned oscillator, and a mixer circuit, said oscillator circuit being inductively coupled to the mixer circuit, said short wave tuner including an `aperiodic antenna circuit, a tuned oscillator circuit and a mixer circuit, said oscillator circuit being capacitively coupled to the mixer circuit, said antenna circuits being common to both subsidiary circuits and means to cause the antenna circuit to become aperiodicrfor use with the short wave tuner.

n 5. 'In a radio receiving circuit comprising a plurality of subsidiary circuits adapted to short Wave and long wave reception, a common amplifier for the subsidiary circuits, saidshort wave Acircuits each comprising an antenna circuit, a.

radio frequency circuit, a mixer and a tuned oscillator, said long wave circuit including a tuned antenna circuit, a tuned radio frequency circuit, a mixer and a tuned oscillator, said subsidiary circuits including a plurality of inductances of different values, said oscillator circuit including a plurality of inductances of different values, said inductances in both circuits being adapted to be selectively connected into the circuits, switching means common to the circuits to render said antenna circuit tuned for long wave reception and aperiodic for short Wave reception and to change thecoupling means between the oscillator and Vthe mixer for short wave reception and for long wave reception. l

6. A superheterodyne radio receiver circuit including an oscillator and a plurality of inductances of different values, a first detector electrically coupled to' the oscillator, means common tothe inductances to tune the same, a single mechanical means adapted to actuate the inductances selectively into operative relationship 'with the oscillator and detector circuit and simultaneously to change the nature and degree of coupling between the oscillator and first detector.

7. In a superheterodyne radio receiver circuit adapted for reception of radio signals of high and low frequency including a low frequency tuner and a high frequency tuner, means common to both tuners for amplifying and rectifying a signal therefrom comprising an intermediate frequency amplifier, a detector, an audio frequency amplifier, and a loud speaker, said low frequency tuner includingan antenna circuit, a tuned radio frequency circuit, a mixer and a tuned oscillator circuit, said high frequency tuner including an antenna circuit and an oscillator circuit and a mixer circuit, said antenna, radio frequency, mixer, and oscillator circuits being common to each of said tuners, electrical coupling means between the mixer and oscillator circuits, and common means to change the coupling means between the mixer circuit and said oscillator circuits.

8. In a radio receiver adapted to receive signais on high and low frequencies including a high frequency tuner and a low frequency tuner, each adapted to furnish a heterodyne signal, and means common to both tuners to amplify, detect and convert said signal into audible sound, said high frequency tuner including an antenna circuit, a radio frequency circuit, a mixer, and a tuned oscillator circuit capacitively coupled to ysaid mixer, said low frequency tuner including an antenna circuit, a tuned radio frequency cir.- cuit, a mixer and a tuned oscillator circuit inductively coupled to the said mixer, common means cooperative with both tuners to selectively engage either tuner into combination with said first mentioned common means when using the receiver on low and high frequency bands respectively to tune the oscillator and radio frequency crcuitssimultaneously by a single dial.

9. In a radio receiver for receiving signals of high and low frequency, a tuner for high frequency and a tuner for low frequency, an antenna circuit common to both tuners, said high frequency tuner circuit including a tuned radio frequency circuit, a mixer and a tuned oscillator circuit capacitively coupled thereto, said low frequency tuner circuit including a tuned radio frequency circuit, a mixer and a tuned oscillator circuit inductively coupled thereto, said tuning means for said radio frequency circuit and said circuit being common to both tuners, means common to both tuners to change the coupling between the radio frequency and oscillator circuits and to-change the tuned inductances of said tune'd circuits to render the tuners operative over different portions of the radio frequency spectrum, and

common meansfor both tuners to amplify the heterodyne signal, rectify the heterodyne signal 'and render the signal audible.

10. In a radio receiver for receiving signals of high and low frequency, including tuners adapted for high and low frequency signals, an antenna circuit common to both tuners and adapted to be tuned for low frequency signals and aperiodic for high frequency signals, said 10W frequency tuner including a tuned radio frequency circuit and a mixer having an inductanoe tuned by a capacitance and a tuned oscillator circuit including an inductance tuned by a capacitance and being inductively coupled to said radio frequency circuit and common means for actuating -said tuning means for said tuned circuits to tune the same simultaneously, said high frequency tuner including a tuned radio frequency tance and a mixer, a tuned oscillator capacitively coupled to said radio frequency circuit and including an inductance tuned by a capacitance, common means for actuating both tuning means for said last mentioned tuned circuits to tune said circuits to be tuned simultaneously, means common to both tuners to amplify, rectify and render a heterodyne signal from either of said tuners and oscillators audible.

ERNEST R. PFAFF. CLIFFORD L. COON. 

